Is Geodiversity Correlated to Biodiversity? A Case Study of the Relationship Between Spatial Heterogeneity of Soil Resources and Tree Diversity in a Western Kenyan Rainforest

Abstract

Interactions of biotic and abiotic factors are critical in determining population dynamics and maintenance of high diversity in tropical rainforests. An investigation was conducted to test the hypothesis that tree species composition and dispersion influence spatial pattern of soil properties on a small scale of meters. Soil variables (pH, EC and total and water extractable (available) K, Ca, Mg and Mn) were highly heterogeneous in both vertical and horizontal dimensions. Available Mn was the most variable (coefficient of variation CV = 76%) parameter and pH the least (CV = 4%). There was an inverse relationship between abundant levels of available cations and heterogeneity. Plots with high heterogeneity in available cations had low tree diversity but there was no evident pattern between total concentration of cations and tree diversity. Tree diversity was negatively correlated to variability of available Mn (r = −0.7). These findings indicate that tree diversity influences soil heterogeneity hence contributing to maintenance of high diversity in tropical rainforests. The results show that the observed soil patterns are caused by geogenic processes as well as processes influenced by vegetation. The raising effect of the vegetation on the elements is expected in the order from Mn, Ca, Mg to K. This vegetation effect indicates the significance of maintaining a closed canopy in tropical rain forests. Geodiversity is thus correlated to biodiversity and needs to be more recognized in ecological research.